I assume that most people who are on this forum ride bicycles to get places most of the time, or at least as often as possible. I ride my bike or walk for probably 80-90% of my local trips. I have a car, but I don't use it more than 1-2 times a month. Last year, I put 3000 mi on the bike and about 200 on the Volvo. I think of the car as a necessary evil: I don't like to drive, and often it's actually much faster and more convenient to ride or take public transportation. However, there are a few things that will make me resort to the car without hesitation, in descending order of urgency:
1. I'm sick, and have to go to work anyway, or at least go to the doctor and buy food. (I could use public transportation for this, but would then risk infecting innocent strangers.)
2. I have to haul something that's too bulky or heavy to be practical on a bicycle. I have hauled science fair display boards and even outboard motors using a bicycle, but these sorts of things are just too much of a PITA on a bike for me to ever do voluntarily again.
3. I have family flying in from out of town.
4. It's really icy or snowy outside. (In this case I won't drive locally, either, I'll just walk. It's not the snow and ice itself that dissuades me, it's Seattle drivers, who often can't even drive in the rain, let alone on ice.)
What are your limits to doing without an internal combustion engine of your very own, or at least a borrowed/rented one?